They do bring back the embargoed packs every now & then, you just have to keep your eyes open for them. As for whats in the packs say there are 40 different things in a pack you get a random 6 of them.
I've got just about all armour set unlocked in collections & all must be on one toon in your legacy. NONE have unlocked if multipul toons have had bits & pieces of the same set.